While the invention is subject to a wide range of applications, it is especially suited for use in reducing the effects of adjacent channel interference to AM Monophonic and AM Stereo systems and will be particularly described in those connections.
There have been many procedures used in the past for reducing the effect of adjacent channel interference, including variable selectivity filters which are manually or automatically operated and audio or IF notch filters which are manually adjusted to sharply discriminate against interference. See, for example, page 517, 518 and 543, 544 K. R. Sturley, "Radio Receiver Design", second edition 1953, John Wiley & Sons, Inc., New York.
Also, there have been many types of systems developed for automatically altering the selectivity of receivers as a function of interference. The selectivity may be varied symmetrically or asymmetrically. Discussion of such systems is provided by Sturley on pages 543 and 544 of his book cited above. The variation in selectivity is provided at intermediate frequency as is the sensing system.
One object of the present invention is to provide inexpensive automatic means for reducing interference while maintaining relatively good frequency response.
A further object is to provide a method for reducing adjacent channel interference which is especially suitable for AM Stereo reception.
The invention also makes use of the so-called "cocktail party effect" to further discriminate against interference. The cocktail party effect is that effect that allows a binaural listener to separate speech arriving from two different talkers and pay more attention to one of the talkers.
A major object of the invention is to allow listeners of AM monophonic and stero signals to take advantage of the "cocktail party effect".